The present invention relates to drug delivery devices for delivering a medicament. In particular, the present invention is directed to an automatic injector assembly for quickly combining two components to form a liquid medicament, and delivering the liquid medicament to an injection site.
An automatic injector is a device that enables intramuscular (IM) or subcutaneous administration of a dosage of medicament. Generally, the medicament is stored as a liquid formulation which is then injected intramuscularly. An advantage of automatic injectors is that they contain a measured dosage of a liquid medicament in a sealed sterile cartridge. As such, automatic injectors allow for quick and simple IM injection of a liquid medicament in emergency situations without the need for measuring dosages. Another advantage of automatic injectors is that the administration of the medicament is accomplished without the user initially seeing the hypodermic needle through which the medicament is delivered, and without requiring the user to manually force the needle into the patient. This is particularly advantageous when the medicament is being self-administered.
There are drawbacks associated with the long-term storage of medicament in a liquid formulation. For instance, some medicaments are not stable in solution and thus have a shorter shelf life than their solid counterparts. To address this concern, automatic injectors have been developed which store the medicament in solid form and mix the solid medicament with a liquid solution immediately prior to injection. These injectors, disclosed for example in U.S Re. issue Pat. No. 35,986, entitled xe2x80x9cMultiple Chamber Automatic Injector,xe2x80x9d (the disclosure of which is incorporated herein specifically by reference), however, require the user of the injector to manually rupture a sealing member between the solid and liquid components and then manually shake the injector body to expedite dissolution of the solid component prior to injection. This increases the time needed to administer a dose of the medicament. However, rapid delivery of the medicament is needed in many emergency medical situations (e.g., nerve gas and chemical agent poisoning). Other wet/dry injection devices have been expensive to manufacture or provided unsatisfactory mixing of components prior to injection. Therefore, there is a need for a cost-effective automatic injector that stores medicament in solid form that does not require manual premixing by the user.
In response to the foregoing challenges, applicants have developed an innovative automatic injection device containing a pre-loaded charge of medicament for automatically administering the medicament upon actuation thereof. The automatic injection device comprises a housing assembly and a chamber disposed within the housing assembly. The interior chamber includes a dry compartment for storing a predetermined charge of dry medicament therein, and a wet compartment for storing a predetermined amount of liquid injection solution therein. A seal structure is disposed to seal the dry compartment from the wet compartment while the injection device is in storage. The seal structure permits the liquid injection solution to pass therethrough and mix with the dry medicament to form a medicament mixture within the chamber during an injection operation. A needle assembly is in communication with the medicament mixture during the injection operation to enable administration of the medicament mixture. A plunger is disposed within the chamber and is movable through the chamber during the injection operation to force the medicament mixture through the needle for administration of the medicament mixture. A stored energy activation assembly is operable to release stored energy that forces the plunger through the chamber during the injection operation. The seal structure is conditionalable in response to operation of the activation assembly to permit the liquid solution to pass therethrough and mix with the dry medicament as aforesaid.